Steps to Reproduce

http://zkfiddle.org/sample/glef8/1-vflex-and-rows-on-listbox
resize the browser window
the horizontal scrollbar (of the listbox) seems to disappear
the listbox content gets recalculated to 640px pushing the scrollbar out of the visible listbox area
see ZK-4264

Current Result

can use both vflex and rows at the same time

Expected Result

error indicating incorrect usage

Debug Info

don't use both rows and vflex="1" at the same time since both are used to determine the height